Magnetrons



July 24, 1962 E T DQwNlNG ET AL 3,046,444

MAGNETRONS Filed April 28, 1959 F/G. I

SMITH /VVE/VTRS EWR r [70W/VIN@ GEORGE E gy Y A rroR/VEY United States PatentO M a corporation of Delaware Filed Apr. 28, 1959, Ser. No. 809,409 Claims. (Cl. S15-39.51)

This invention relates to a magnetron-type electron discharge device, and, more particularly, to means for supporting a cathode assembly in a magnetron-type electron discharge device.

Magnetron electron discharge devices vare well known which comprise a cathode structure, an anode ystructure spaced from and surrounding said cathode structure and incorporating several cavity resonators, and also means for establishing a magnetic field transverse to the electron path between the cathode and anode structures. When a proper voltage is applied between the cathode and anode structures of such a device, and when the magnetic field is adjusted to an appropriate value relative to the electric field created by 4the yaforesaid voltage, oscillatory energy is generated whose frequency is determined primarily by the geometry of the physical elements comprising the cavity resonators.

-In some applications, magnetrons are subjected to severe vibration and shock during operation. ln magnetrons of the prior art, wherein the cathode is supported at a single point, the cathode assembly may be considered mechanically to be a cantilever beam. When such a device is subjected to shock and vibration, movement of the cathode invariably occurs, whereupon undesirable amplitude and frequency modulation of the magnetron output takes place. If the free end of the cathode assembly is supported in some manner, movement of the cathode assembly is reduced, together with the accompanying undesirable modulation.

One type of cathode support previously resorted to consists of a ceramic washer placed around the free end of the cathode assembly and attached to one of the magnetron pole pieces. This cathode mounting arrangement, although an improvement over the cantilever-type cathode mounting arrangement, has certain disadvantages. There is a considerable voltage gradient along the ceramic washer of the prior art, particularly in the case of high voltage tubes, because of the relatively short leakage path along the insulating washer interposed between the anode and cathode; instability resulting from excessive current leakage over the insulating washer, or even tube breakdown owing to arcing, often occurs. Although this trouble may be reduced somewhat by increasing the diameter of the insulating washer, this can be yachieved only be reducing the lsize of the poleV piece in the region of the washer or by increasing the diameter of the pole piece assembly. If the pole piece is cut away, the reluctance of the pole pieces is increased, with `a subsequent reduction in magnetic field strength. If, on the other hand, the ydiameter of the pole piece yis increased, the bulk of the magnetic assembly is unduly increased and, in fact, the entire tube may have to be made larger to accommodate such an enlarged magnet assembly.

Moreover, the ceramic washer of the prior art is eX- posed to electron-emissive material evaporated from the cathode during tube operation. This electrically-conductive material, which gets past the cathode end shields, is deposited upon the ceramic washer and forms an `electrically-conductive film on the washer. This film eventually causes an electrical short circuit between the cathode and the anode (which is electrically connected to the magnetic pole pieces).

When certain cathode materials, such as nickel, are

3,046,444 Patented July 24, 1962 ICC used which have a greater temperature coefficient of expansion than ceramic, there is a pronounced tendency for binding to occur between the ceramic washer of the prior art and the cathode 'sleeve which is inserted within the ceramic Washer. Such binding is undesirable, since it is necessary, in order to prevent bending or other distortion of the cathode assembly, that the cathode be free to slide in the ceramic support during thermal expansion and contraction.

Because of the relatively short path presented by the ceramic washer of the prior art between the cathode and the pole pieces (and the anode block), the thermal losses by conduction are relatively high, thus increasing the heater power requirements correspondingly.

In accordance with this invention, an elongated ceramic member of relatively small outer dimension and crosssectional area is inserted in the tail end of either the cathode sleeve or an extension thereof. A metal or ceramic washer is attached to the other end of the ceramic member and this washer is bonded to the magnetic pole pieces or anode. This cathode support has several advantages over the cathode support of the prior art, previously referred to. 'Ihe ceramic rod has a small radial dimension, being less than that of the cathode sleeve, or at least smaller than that of the cathode end shields, if any. Consequently, little or no electron-emissive material evaporating from the active surface of the cathode will be deposited upon lthe ceramic. Inasmuch as the ceramic rod can be made of considerable length without unduly complicating tube design, the voltage gradient in the ceramic rod may be relatively small and the leakage path `along the ceramic rod may be comparatively long. Since the ceramic rod is positioned inside the cathode sleeve, binding between the rod and the cathode sleeve-owing to thermal expansion and contraction of the rod and sleeve-will be minimized and the necessary capability for relative motion of the cathode Vand cathode support is maintained. A material, such as molybdenum, which has substantially the lsame thermal coefficient of expansion as the ceramic rod, will not bind with the rod; furthermore, any tendency for the rod to fit too loosely in the cathode sleeve will be prevented. `Since the ceramic rod is of considerable length and of relatively small cross-sectional area, thermal losses from the cathode by way of conduction are reduced; moreover, any variation in the degre of contact resistance between the cathode and the ceramic rod will constitute a correspondingly smaller portion of the total thermal resistive path, whereby the effect of contact variation is reduced. It has been found that considerable reduction in heater power required for starting the magnetron can be achieved with the cathode support Aaccording to the invention.

Other objects and advantages of this invention will become apparent -as the description thereof progresses, reference being had to the accompanying drawing wherein:

FIG. 1 is a central cross-sectional View of a magnetron incorporating Ia cathode support according to the invention; and

FIG. 2 is a detail View illustrating a manner of modifying the cathode support shown in FIG. 1.

Referring to the drawing, refernce numeral 10 designates an electron discharge device of the magnetron type having an anode structure 12 of well known construction 4which includes a cylindrical envelope member 13 of an electrically-conductive material and a plurality of radially disposed, inwardly extending anode mem-bers 14 in the form of electrically-conductive vanes attached to member 13. Each pair of adjacent anode members, together with tha-t portion of the cylindrical member included therebetween, at least partially define a cavity resonator; these resonators are electrically intercoupled in the normal manner. Alternate anode members 14 are connected together -adjacent their innermost ends by straps 16 in order to prevent spurious oscillation of the magnetron in undesired modes. The upper and lower ends of the tube are shielded hermetically by means of respective pole shoes 18 and 19 of magnetic material attached to anode cylinder 13. The pole shoes 18 and 19 are connected to pole pieces 21 and 22, respectively. A U-shaped magnet 24, partially shown in FIG. l, is held a-gainst the pole pieces 21 and 22 for providing the necessary magnetic eld. Output energy may be coupled from the magnetron to a wave guide 26 by means of a slot, not shown, cut in the anode cylinder 13 between any two adjacent anode members 14. The anode cylinder l13 may include a ilanged portion 13 to which the wave guide 26 may be attached. An exhaust tip-olf 27 is connected toa disoidal member 28 which, in turn, is connected to lower pole piece 22; this tip-olf provides a means for exhausting the magnetron tube 10. A member 29 attached to lower pole piece 22 serves to protect the exhaust tip-olf 27 from damage.

A cathode structure 30 is positioned concentric with anode structure 12 and includes a cathode sleeve 31 which may, for example, be made of nickel and which is provided with integral end shields 31a and 31b. The portion of sleeve 31 facing the extremities of the anode members 14 is coated with an electron-emissive material, in the well known manner. The cathode structure 30 further includes a heater element 32 positioned within the cathode sleeve 31 and connected at one end thereto. The other end of heater element 32 is attached, as by welding, to a heater lead-in wire 33 which passes out of the tube envelope through a tubular member 34 fastened at one end to the upper end of cathode sleeve 31. The heater lead-in wire 33 may be supported within the tubular member 34 by electrically insulating beads 35. A short metal tube 36 is attached to upper pole piece 21 at one end, while a glass or ceramic seal 37 is attached to the other end of tube 36. A metal thimble 38, which is brazed to a metal disk 39, is sealed to glass seal 37 and to the outer periphery of tubular member 34. A glass bead 40 `at the upper end of tubular member 34 completes the hermetic seal for the cathode structure. The cathode-heater supply voltage may be furnished by way of circuit leads, not shown, which may be connected to the heater lead-in wire 33 and the disk 39, respectively.

A cathode sleeve extension in the form of a short tube 42 and made, for example, of molybdenum, is brazed to the lower end of cathode sleeve 31. Slots 43 may be provided in the periphery of tube 42 to prevent possible deformation of the tube during brazing owing -to difterences in thermal coefficients of expansion of the nickel cathode sleeve and the molybdenum tube. The cathode support structure 30 includes an elongated ceramic rod 44 securely attached at one end to metal washer 45 and slidably mounted at the other end to the tubular extension 42 of the cathode sleeve so as to support the cathode and prevent radial movement thereof. 'Ihe metal washer 45 is sealed to lower pole piece 22 and is provided with apertures 46 to permit evacuation of the tube. The washer 45, instead of being made of metal, such as kovar, may be made of ceramic, particularly where a slightly larger leakage path between anode and cathode is desirable. A metal washer is somewhat more convenient, however, since a metal washer may be sealed more readily to the metal pole piece 22 than a ceramic washer.

As indicated in FIG. 2, it is possible to insert the ceramic rod 44 of the cathode support structure 30 directly into the cathode sleeve 31, provided that the cathode sleeve is made of a substance, such as molybdenum, which (l) has approximately the same thermal coefficient of expansion as the ceramic Irod and which (2) will not cause binding to occur between the cathode sleeve and the elongated ceramic rod 44.

This invention is not limited to the particular details of construction, materials and processes described, as many equivalents will suggest themselves to those skilled in the art. It is accordingly desired that the appended claims be given a broad interpretation commensurate with the scope of the invention within the art.

What is claimed is:

1. In a magnetron having an anode structure and having a cathode whose longitudinal axis is coincident with the longitudinal axis of said magnetron, an elongated electrically insulating member arranged parallel to said longitudinal axis and slidably supporting said cathode at one end thereof, said member having substantially smaller cross wise dimensions than said one end of said cathode and an element attached to said member, said element extending substantially perpendicular to said longitudinal axis and being supported by said anode structure.

2. In a magnetron having an anode structure and a cathode, an elongated electrically insulating member slidably supporting said cathode at one end thereof, said member having substantially smaller cross wise dimensions than said one end of said cathode, and a discoidal element attached to said member and supported by said anode structure.

3. In a magnetron having an anode structure and a cathode, means for supporting said cathode at both ends thereof with respect to said anode structure, said means for supporting including an elongated electrically insulating member movably joined to said cathode adjacent one end of said member, said member having substantially smaller cross wise dimensions than said cathode and an element attached to said member adjacent the other end of said member supported by said anode Structure.

4. In a magnetron having an anode structure and a cathode, means for supporting said cathode at both ends thereof with respect to said anode structure, said means for supporting including an elongated electrically insulating member slidably engaging said cathode adjacent one end of said member, and an element attached to said member adjacent the other end of said member.

5. In an electron discharge device having a magnetic field-producing structure, an anode structure and a cathode for directing electrons in the region between said cathode and said anode structure, an elongated electrically insulating member slidably engaging said cathode adjacent one end of said member, and an element attached to a portion of said magnetic field-producing structure and to said member adjacent the other end of said member.

6. In an electron discharge device having a magnetic field-producing structure, an anode structure and a cathode for directing electrons in the region between said cathode and said anode structure, an elongated electrically insulating member slidably engaging said cathode adjacent one end of said member, said member having an outer dimension less than that of said cathode, and an element attached to a portion of said magnetic field-producing structure and to said member adjacent the other end of said member.

7. In an electron discharge device having an assembly including an anode structure and at least a portion of a magnetic eld-producing structure, and a cathode for directing electrons in the region between said cathode and said anode structure, said cathode including end shields extending outwardly therefrom, an elongated electrically insulating member slidably engaging said cathode adjacent one end of said member, said member having an outer dimension less than that of said cathode end shields, and an element attached to a portion of said assembly and to said member adjacent the other end of said member.

8. In an electron discharge device having an assembly including an anode structure and at least a portion of a magnetic field-producing structure, and a cathode for directing electrons in the region between said cathode and said anode structure, an elongated electrically insulating member slidably engaging said cathode adjacent one end of said member, said member having an outer dimension less than that of said cathode, and an element extending substantially perpendicular to said member and attached to a portion of said assembly and to said member adjacent the other end of said member.

9. In a magnetron having an anode structure and a cathode structure and means for producing a magnetic eld transverse to `said region, said anode structure and at least a portion of said magnetic field-producing means forming an integrally mounted assembly, said cathode structure including a tubular portion, an elongated electrically insulating member disposed along the longitudinal axis of said magnetron and having one end slidably inserted within said tubular portion, and an element disposed substantially perpendicular to said member `and attached -to `a portion of said assembly and to said member adjacent the other end thereof, the lateral extremities of said member being disposed nearer said longitudinal axis than the lateral extremities of said cathode structure.

10. In a magnetron having an anode structure and a cathode structure and means for producing a magnetic eld transverse to said region, said anode structure and at least a portion of said magnetic field-producing means forming an integrally mounted assembly, said cathode structure including a tubular extension, `an elongated electrically insulating member disposed along the longitudinal axis of said magnetron and having one end slidably inserted Within said tubular extension, and an element disposed substantially perpendicular to said member and attached -to a portion of said assembly and to said member adjacent the other end thereof, the lateral extremities of said member being disposed nearer said longitudinal axis than the lateral extremities of said cathode structure, said tubular extension having a thermal coefficient of expansion substantially equal to that of said member.

References Cited in the le of this patent UNITED STATES PATENTS 1,666,010 Hawadier Apr. 10, 1928 2,199,956 Marden May 7, 1940 2,412,824 MacArthur Dec. 17, 1946 2,414,605 Okress Ian. 2l, 1947 2,424,805 De Walt July 29, 1947 2,444,418 Bondley July 6, 1948 2,698,913 Espersen Jan. 4, 1955 OTHER REFERENCES Microwave Magnetrons, Collins, page 792 relied upon, McGraw-Hill, 1948, 

